1. Field of the Invention
The present invention relates to a charged particle beam irradiation method, a method of manufacturing a semiconductor device and a charged particle beam apparatus, and is directed to, for example, specifying of an electron beam irradiation position in scanning with an electron beam.
2. Related Background Art
For observing a subject by use of a charged particle beam apparatus, for example, a scanning electron microscope (SEM), raster scanning is performed with an electron beam emitted from an electron gun through a scanning deflector to detect secondary electrons, reflected electrons and back scattering electrons (hereinafter referred to as secondary electrons and the like) produced from the surface of the subject due to electron beam irradiation, and an obtained signal is then processed to acquire an image (SEM image) based on the electron beam irradiation. The raster scanning is characterized in that the position for irradiation of the electron beam continuously moves, for example, from left to right in a screen. In accordance with image display that has heretofore been generally used, a secondary electron signal acquired at a scanning position on the subject is transmitted to elements (pixels) for image display to display a two-dimensional image. The elements for image display are generally arranged equally in horizontal and vertical directions, and in the raster scanning, horizontal scanning is followed by vertical scanning, and the horizontal scanning is again performed, which operation is repeated, as shown in FIG. 8A.
However, when irregular shapes such as an LSI pattern or parts of different materials are scanned with the electron beam, charges may be increased depending on the shape of the pattern and the scanning direction of the electron beam, thus causing contrast variance in the SEM image. Moreover, between an edge perpendicular to the scanning direction of the electron beam and an edge parallel with the scanning direction, a difference may be made in contrast and image resolution at an edge portion. This is apparent from line profiles representing grayscale values of the edge portions. For example, in the scanning along a D0-D1 direction perpendicular to a pattern edge EP1 in FIG. 8A, its line profile indicates a sharp rise in contrast as shown in FIG. 8C, while in the scanning along a C0-C1 direction slanted with respect to the pattern edge EP1, its line profile indicates a gentle rise as shown in FIG. 8B.
Thus, a difference is made in the resolution of the pattern edges depending on the scanning direction even with the same sectional shape. In LSI patterns such as simple line patterns that have been conventionally measured, there has not been a specific problem with the resolution of the edge portions because an image is obtained in a scanning direction perpendicular to a longitudinal direction of the pattern. However, along with the miniaturization and complication in the recent LSI patterns, one-dimensional measurement of the LSI patterns and the like alone does not enable adequate evaluation of shapes and process management in addition to a stronger tendency to make two-dimensional shape evaluation by use of the two-dimensional image obtained by the raster scanning. Items in this shape evaluation includes, for example, the area and circumferential length of a hole pattern and the degree of roundness at pattern corners, as well as the conventional line width of the line pattern.
As described above, the raster scanning might cause the contrast variance depending on the pattern shape and the scanning direction and changes in resolution due to the direction of the edge. Therefore, the two-dimensional shape evaluation is implemented from the image obtained by the raster scanning, a measurement result may include the influence of the scanning direction, in which case an accurate measurement result can not be obtained. Thus, a scanning technique other than the raster scanning is required in order to obtain an image without the influence of the scanning direction.
One of the scanning techniques without the influence of the scanning direction is random scanning (e.g., Japanese Patent Publication Laid-open No. 5-151921). One characteristic of this technique is that irradiation position information signals which specify an electron beam irradiation position in a scanning plane to be scanned with the electron beam are sequentially output so that each of them randomly specifies the irradiation position, and the electron beam is applied to the irradiation positions corresponding to the output irradiation position information signals.
However, if the whole irradiation area for the electron beam corresponding to measurement magnification is randomly scanned, there is a problem that a significant amount of time is needed to obtain an image for measurement.
Furthermore, the problem of scanning perpendicularly to the pattern edge is that, because the elements for image display are arranged equally in horizontal/vertical directions in the ordinary image display, if scanning is performed with the electron beam in an oblique direction E0-E1 to indicate an image signal as shown in FIG. 9A, its line profile indicates a sharp rise as shown in FIG. 9B, but lattices in the oblique direction do not link together to cause a lack of information in the image signal.
Still further, in order to measure the hole patterns, such a technique has also been put into practical use wherein scanning is performed with the electron beam in a diametric direction of the hole and the measurement is performed after conversion into a polar coordinate system. However, the polar coordinate system is a technique which is applicable only to the hole patterns and not applicable to an arbitrary pattern shape.